Causes could be include the harvest regulations governing sport anglers and Chippewa netters, the explosion of zebra mussels in the lake, improved water clarity or a potential lack of prey fish such as perch and tullibees.

Pereira says it's too early to say if the DNR might tighten regulations on the lake in east-central Minnesota.

Business owners say further restrictions could undercut tourism. DNR and tribal fisheries researchers will discuss the lake next week.